More than 1,000 Miami-Dade residents failed to cast a vote, or had a vote that did not count, in Tuesday's strong-mayor referendum — a tiny percentage of the overall tally but still worrisome to some voter advocates watching the single-question ballot.

Though the difference wasn't anywhere near enough to swing the election — unlike November's disputed Sarasota election to replace Rep. Katherine Harris — the “undervotes” are still a concern, with election-reform advocates leery of touch-screen machines that do not leave paper trails.

“People don't go there and forget what they went for and walk out. I don't buy that,” said Sandy Wayland, president of the Miami-Dade Election Reform Coalition.

Still, what makes these undervotes different and less sensational than others is that Miami-Dade absentee voters on optical-scan paper ballots cast nearly as high a percentage of undervotes.

an independent study that cites new evidence of machine failure in Sarasota County and concludes that misleading ballot design, voter turnoff and other theories do not account for the “extraordinarily high undervote rate” in the county.

The authors of the report, who said they performed a statistical analysis of electronic ballot and “event log data” from the November election, said they were “unable to propose a convincing mechanism based on voter, machine or ballot characteristics that completely explains the phenomenon.

“In a nutshell,” wrote authors David Dill and Walter Mebane, “the excessive CD-13 undervote rate in Sarasota County is not yet well-understood and will not be understood without further investigation.”